The present invention relates to a lens device for an illumination assembly, in particular for a variable working distance. Moreover, the present invention relates to an illumination assembly for a measuring machine for measuring a workpiece by means of an optical sensor. Moreover, the present invention relates to a coordinate measuring machine for measuring a workpiece by means of an optical sensor. Moreover, the present invention relates to a method for modifying an illumination working distance, in particular of a dark field top light illumination of a coordinate measuring machine.
By way of example, illumination modules for coordinate measuring machines are known from the document EP 0 362 625 A2.
Coordinate measuring machines are generally known in the prior art. They serve for checking workpieces, for example as part of quality assurance, or for ascertaining the geometry of a workpiece completely as part of what is known as “reverse engineering.” Moreover, multifarious further application possibilities are conceivable.
In coordinate measuring machines of this type, different types of sensors may be used to capture the coordinates of a workpiece to be measured. By way of example, sensors that measure in tactile fashion are known in this respect, as are sold, for example, by the applicant under the name “VAST”, “VAST XT” or “VAST XXT.” Here, the surface of the workpiece to be measured is probed with a stylus, the coordinates of said stylus in the measurement space being known at all times. Such a stylus may also be moved along the surface of a workpiece, and so a multiplicity of measurement points may be captured at set time intervals during such a measuring process within the scope of a so-called “scanning method”.
It is moreover known to use optical sensors that facilitate contactless capturing of the coordinates of a workpiece. One example of such an optical sensor is the optical sensor sold by the applicant under the name “ViScan”.
The sensors may then be used in different types of measurement constructions. One example of such a measurement construction is the product “O-INSPECT” by the applicant. In an appliance of this type, both an optical sensor and a tactile sensor are used to carry out various examination tasks on a machine and ideally with a single setup of a workpiece to be measured.
Sensor systems comprising optical sensors are becoming increasingly more important in coordinates metrology. Here, optical sensors are distinguished, in particular, by a high speed of the measuring process. In this way it is possible to carry out many examination tasks, for example in medical engineering, plastics technology, electronics and precision engineering. Naturally, various other application options are also conceivable.
Conventionally, the optical sensor head or the optical sensor is connected to a carrier system which supports and moves the optical sensor system. Various carrier systems are known, for example portal systems, stand systems, horizontal arm systems and arm systems, and all types of robotic systems. Here, the carrier systems may moreover comprise system components which facilitate a positioning of the sensor head which is as flexible as possible. An example for this is the articulation from the applicant sold under the name “RDS”. Moreover, various adapters for connecting the various system components of the carrier system among themselves and with the sensor system may be provided.
Moreover, it is conventional in coordinate metrology that work may be conducted with different types of illumination when measuring objects. By way of example, provision may be made of reflected light illumination which, for example, may be configured as bright field illumination or as dark field illumination. By way of example, the corresponding optical sensors comprise a video camera and/or an image camera and appropriate illumination for the workpiece. Moreover, a fixed imaging optical unit is usually provided, said fixed imaging optical unit imaging the workpiece to be measured onto the camera or the optical sensors of the camera. Here, in general, provision is made of specific optical sensors comprising fixedly integrated illuminations and imaging optical units for each application or each type of measurement.
By way of example, the document EP 0 362 625 A2 exhibits an interchangeable front optical unit for an optical sensing probe. This front optical unit is embodied for a specific working distance and a specific illumination type. Moreover, it comprises the whole lens which images light rays reflected by the workpiece onto the optical sensor.
However, such a front optical unit is relatively heavy on account of the optical elements for imaging purposes and has a relatively large volume. Moreover, such a front optical unit is only usable for a specific application, i.e. at a specific working distance and for a specific illumination type.
Moreover, documents EP 0 385 262 A2 and EP 1 373 827 B1 likewise specify illumination devices for coordinate measuring machines, said illumination devices, firstly, comprising imaging optical units and, secondly, comprising e.g. swivelable or movable illumination elements with a relatively complex embodiment in order to adjust the illumination to different working distances. However, this also results in a relatively complex structure of such illumination elements and, possibly, a relatively high weight and volume which makes regulating the optical sensor head more difficult on account of the higher inertia connected therewith, in particular in the case of fast measuring processes.
Document WO 2013/167168 A1 shows an illumination module for a coordinate measuring machine for measuring a workpiece by means of an optical sensor, wherein the illumination module comprises a main body with a sensor side and a workpiece side, wherein the illumination module comprises, on the main body, at least one illumination arrangement for illuminating the workpiece and wherein the at least one illumination arrangement has an emission characteristic with an emission angle and a light-intensity curve within the emission angle, wherein the light-intensity curve of the at least one illumination arrangement is asymmetric within the emission angle.
The workpiece should be illuminated in different ways dependent on the workpiece to be examined and the measuring method applied by means of the optical sensor. In the process, it is possible, for example, for a working distance, at which the measurement process is undertaken, to vary. Moreover, an illumination with different angles of incidence on a surface of the workpiece may be desired in certain circumstances. Therefore, in practice, illumination assemblies should either be interchanged or an illumination assembly comprises a plurality of alternately switchable light sources which provide different types of illumination. However, such arrangements make an illumination assembly heavier on the one hand and, on the other hand, increase the costs of an illumination assembly. However, it is desirable, as a matter of principle, to be able to provide illuminations at different working distances and/or with different angles of incidence by means of one illumination assembly. Particularly in the case of a desired reflected light dark field illumination at a variable working distance, it is desirable to be able to set different angles of incidence as easily as possible.